Hi,
Can you explain the problem with some information ?
Like giving the payment plugin you are using, for example.
Most of time, when you are in "test" mode, you have to use "test cards".
We generally use the card 4111 1111 1111 1111 but this card does not work with every payment gateways. That's why having some useful information about your environment can be very helpful, to help you.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.